Electrolyzers of filterpress type consist of a stack of elementary electrolytic cells, each elementary cell consisting of two parallel metallic electrode plates separated from one another so as to leave a gap which in turn is separated into two compartments by a plane diaphragm parallel with the electrodes. The compartment situated between the positive electrode or anode and the diaphragm is called the anodic compartment and the compartment situated between the negative electrode or cathode and the diaphragm is called the cathodic compartment. The electrolyte is made to flow on the one hand into the anodic compartment, the electrolyte then being referred to as anolyte, and on the other hand into the cathodic compartment, the electrolyte in it then being referred to as catholyte. In general each elementary cell is placed upright on its edge and the electrolyte flows from the bottom upwards; the liquid-gas mixtures due to the electrolytic reactions in the anodic compartment on the one hand and in the cathodic compartment on the other are then collected in the top portion of the electrolytic cell, whence the cathodic mixture and the anodic mixture are discharged separately.
In an electrolyzer of filterpress type consisting of a stack of a very large number of elementary cells, the following stacking will be found:
a metal plate connected to the negative voltage generally consisting of the earth of the installation; PA1 a cathodic gap; PA1 a diaphragm; PA1 an anodic gap; PA1 a metal plate insulated electrically, of which the face turned towards the said anodic gap and charged by influence with positive electricity consequently forms the anode of the first cell, while the other face, necessarily charged with negative electricity by preservation of electricity, forms the cathode of the second cell; PA1 a second cathodic gap; PA1 a second diaphragm; PA1 a second anodic gap; PA1 a second metal plate insulated electrically; PA1 and so on until the last metal plate which is connected to the positive pole of the electric supply to the electrolyzer, and which forms the last anode. In practice the metal plate situated at about every fifty cells is a thick plate which enables the electrolyzer to be formed mechanically of a set of packs of cells. PA1 firstly this supply and discharge is effected under pressures having a dynamic component which is much higher PA1 secondly this type of feed by three or four distribution channels parallel with the axis of the stack introduces, PA1 at least one electrolyte inlet circuit common to the said set, from which leave channels feeding separately each anodic compartment and each cathodic compartment; PA1 an anolyte outlet circuit common to the said set, at which terminate channels connected separately to each anodic compartment; PA1 a catholyte outlet circuit common to the said set, at which terminate channels connected separately to each cathodic compartment;
Hence, in an electrolyzer of this type, the electrolyte is introduced into the bottom portion of each compartment by means of at least one inlet channel of small cross-section, and is later discharged from the said compartment at the top portion of it, likewise by means of at least one discharge channel of small cross-section. These channels are given a small cross-section within the bounds of hydraulic essentials, so that the leakage current through them is as low as possible.
Furthermore, in prior art electrolyzers, each of the cell discharge channels opens into a discharge channel common to all of the cells, one for the catholyte and one for the anolyte, each of these channels being parallel with the axis of the stack. Similarly, each of the inlet channels leaves, as the case may be, either only one common electrolyte inlet channel (see the aforementioned French Pat. No. 2.448.583), likewise parallel with the axis of the stack, or a first common channel of the same type but intended for the anodic compartments and a second channel of the same type but intended for the cathodic compartments (see the aforementioned French Pat. No. 2.448.581.).
These conventional electrolyte supply and discharge devices display two disadvantages prejudicial to the performance of the electrolyzer:
for the cells near the inlet or outlet from the electrolyzer than for the cells which are remote from them; consequently the flows and as a result the differential pressures and the heating are not identical for all of the cells in the stack, which is very prejudicial not only to the performance of the electrolyzer but also to its length of life;
from the electrical point of view, three or four resistances of low value in parallel across the electrolyzer, in which a leakage current flows which causes a reduction in the performance of the electrolyzer by reduction of the useful current.